152 research outputs found
Conductivity sum rule, implication for in-plane dynamics and c-axis response
Recently observed -axis optical sum rule violations indicate non-Fermi
liquid in-plane behavior. For coherent -axis coupling, the observed flat,
nearly frequency independent -axis conductivity implies
a large in-plane scattering rate around and therefore any
pseudogap that might form at low frequency in the normal state will be smeared.
On the other hand incoherent -axis coupling places no restriction on the
value of and gives a more consistent picture of the observed sum rule
violation which, we find in some cases, can be less than half.Comment: 3 figures. To appear in PR
Common DNA Variants Accurately Rank an Individual of Extreme Height
Polygenic scores (or genetic risk scores) quantify the aggregate of small effects from many common genetic loci that have been associated with a trait through genome-wide association. Polygenic scores were first used successfully in schizophrenia and have since been applied to multiple phenotypes including multiple sclerosis, rheumatoid arthritis, and height. Because human height is an easily-measured and complex polygenic trait, polygenic height scores provide exciting insights into the predictability of aggregate common variant effect on the phenotype. Shawn Bradley is an extremely tall former professional basketball player from Brigham Young University and the National Basketball Association (NBA), measuring 2.29 meters (7′6″, 99.99999th percentile for height) tall, with no known medical conditions. Here, we present a case where a rare combination of common SNPs in one individual results in an extremely high polygenic height score that is correlated with an extreme phenotype. While polygenic scores are not clinically significant in the average case, our findings suggest that for extreme phenotypes, polygenic scores may be more successful for the prediction of individuals
Anomalous fluctuations of the condensate in interacting Bose gases
We find that the fluctuations of the condensate in a weakly interacting Bose
gas confined in a box of volume follow the law . This anomalous behaviour arises from the occurrence of infrared
divergencies due to phonon excitations and holds also for strongly correlated
Bose superfluids. The analysis is extended to an interacting Bose gas confined
in a harmonic trap where the fluctuations are found to exhibit a similar
anomaly.Comment: 4 pages, RevTe
FERMION ZERO MODES AND BLACK-HOLE HYPERMULTIPLETS WITH RIGID SUPERSYMMETRY
The gravitini zero modes riding on top of the extreme Reissner-Nordstrom
black-hole solution of N=2 supergravity are shown to be normalizable. The
gravitini and dilatini zero modes of axion-dilaton extreme black-hole solutions
of N=4 supergravity are also given and found to have finite norms. These norms
are duality invariant. The finiteness and positivity of the norms in both cases
are found to be correlated with the Witten-Israel-Nester construction; however,
we have replaced the Witten condition by the pure-spin-3/2 constraint on the
gravitini. We compare our calculation of the norms with the calculations which
provide the moduli space metric for extreme black holes.
The action of the N=2 hypermultiplet with an off-shell central charge
describes the solitons of N=2 supergravity. This action, in the
Majumdar-Papapetrou multi-black-hole background, is shown to be N=2 rigidly
supersymmetric.Comment: 18 pages, LaTe
Analytic structure factors and pair-correlation functions for the unpolarized homogeneous electron gas
We propose a simple and accurate model for the electron static structure
factors (and corresponding pair-correlation functions) of the 3D unpolarized
homogeneous electron gas. Our spin-resolved pair-correlation function is built
up with a combination of analytic constraints and fitting procedures to quantum
Monte Carlo data, and, in comparison to previous attempts (i) fulfills more
known integral and differential properties of the exact pair-correlation
function, (ii) is analytic both in real and in reciprocal space, and (iii)
accurately interpolates the newest, extensive diffusion-Monte Carlo data of
Ortiz, Harris and Ballone [Phys. Rev. Lett. 82, 5317 (1999)]. This can be of
interest for the study of electron correlations of real materials and for the
construction of new exchange and correlation energy density functionals.Comment: 14 pages, 5 figures, submitted to Phys. Rev.
History of climate modeling
The history of climate modeling begins with conceptual models, followed in the 19th century by mathematical models of energy balance and radiative transfer, as well as simple analog models. Since the 1950s, the principal tools of climate science have been computer simulation models of the global general circulation. From the 1990s to the present, a trend toward increasingly comprehensive coupled models of the entire climate system has dominated the field. Climate model evaluation and intercomparison is changing modeling into a more standardized, modular process, presenting the potential for unifying research and operational aspects of climate science. WIREs Clim Change 2011 2 128–139 DOI: 10.1002/wcc.95 For further resources related to this article, please visit the WIREs websitePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79438/1/95_ftp.pd
Analysis of Stochastic Strategies in Bacterial Competence: A Master Equation Approach
Competence is a transiently differentiated state that certain bacterial cells reach when faced with a stressful environment. Entrance into competence can be attributed to the excitability of the dynamics governing the genetic circuit that regulates this cellular behavior. Like many biological behaviors, entrance into competence is a stochastic event. In this case cellular noise is responsible for driving the cell from a vegetative state into competence and back. In this work we present a novel numerical method for the analysis of stochastic biochemical events and use it to study the excitable dynamics responsible for competence in Bacillus subtilis. Starting with a Finite State Projection (FSP) solution of the chemical master equation (CME), we develop efficient numerical tools for accurately computing competence probability. Additionally, we propose a new approach for the sensitivity analysis of stochastic events and utilize it to elucidate the robustness properties of the competence regulatory genetic circuit. We also propose and implement a numerical method to calculate the expected time it takes a cell to return from competence. Although this study is focused on an example of cell-differentiation in Bacillus subtilis, our approach can be applied to a wide range of stochastic phenomena in biological systems
Critical behavior of the three-dimensional XY universality class
We improve the theoretical estimates of the critical exponents for the
three-dimensional XY universality class. We find alpha=-0.0146(8),
gamma=1.3177(5), nu=0.67155(27), eta=0.0380(4), beta=0.3485(2), and
delta=4.780(2). We observe a discrepancy with the most recent experimental
estimate of alpha; this discrepancy calls for further theoretical and
experimental investigations. Our results are obtained by combining Monte Carlo
simulations based on finite-size scaling methods, and high-temperature
expansions. Two improved models (with suppressed leading scaling corrections)
are selected by Monte Carlo computation. The critical exponents are computed
from high-temperature expansions specialized to these improved models. By the
same technique we determine the coefficients of the small-magnetization
expansion of the equation of state. This expansion is extended analytically by
means of approximate parametric representations, obtaining the equation of
state in the whole critical region. We also determine the specific-heat
amplitude ratio.Comment: 61 pages, 3 figures, RevTe
Improved high-temperature expansion and critical equation of state of three-dimensional Ising-like systems
High-temperature series are computed for a generalized Ising model with
arbitrary potential. Two specific ``improved'' potentials (suppressing leading
scaling corrections) are selected by Monte Carlo computation. Critical
exponents are extracted from high-temperature series specialized to improved
potentials, achieving high accuracy; our best estimates are:
, , , ,
. By the same technique, the coefficients of the small-field
expansion for the effective potential (Helmholtz free energy) are computed.
These results are applied to the construction of parametric representations of
the critical equation of state. A systematic approximation scheme, based on a
global stationarity condition, is introduced (the lowest-order approximation
reproduces the linear parametric model). This scheme is used for an accurate
determination of universal ratios of amplitudes. A comparison with other
theoretical and experimental determinations of universal quantities is
presented.Comment: 65 pages, 1 figure, revtex. New Monte Carlo data by Hasenbusch
enabled us to improve the determination of the critical exponents and of the
equation of state. The discussion of several topics was improved and the
bibliography was update
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